I've played a handful of the spin-offs in the past. I finished FFX-2, FFTA, and probably a couple other minor games. I've dabbled in FFTA2, Theatrhythm, All The Bravest, Crystal Defenders, Crystal Chronicles, and many more without completing them.
If you can't tell by now, I love Final Fantasy. It's one of the only series that I've had a consistent passion for over the years.
I plan on starting to get into these spinoff titles soon. So if you see a post with "The Final Fantasy Project Sidequests" in the title you'll know what to expect. I want to play around with as many spin-offs as I can. Since I know they're very hit-or-miss I don't plan on completing them all, but I would like to get a taste of as many as I can get my hands on. I mean, look how many there are.
Click to embiggen this fantastic flowchart
Let me know if you have any particular suggestions for my Final Fantasy spin-offs exploration. You can tweet at me @grnmushroom or, as always, you can leave a comment below.